Over the past several years, photographic manufacturers have focused on ways of conserving a valuable silver resource by lowering the coated weight of light-sensitive silver halide in photographic elements (S. Honjo, J. Imaging Tech., 15, 182 (1989)). However, it has been difficult to obtain a low silver-containing light sensitive material that does not compromise important image qualities like sharpness, speed, or graininess (European Patent Publication 0 629 909 ).
In Antoniades et al., U.S. Pat. No. 5,250,403, there are described photographic elements that use ultrathin tabular grain emulsions (less than 0.07 microns thick) in the top-most layer that provide distinct improvements in the specularity of the transmitted light and, thereby, an improvement in the acutance of underlying layers. In Sowinski et al., U.S. Pat. No. 5,219,715, there are described photographic elements having low coverage of certain tabular grain silver halide emulsions. However, the use of such ultrathin tabular grain emulsions is reported by one of the inventors in the above Sowinski patent to lead to significant speed losses (A. E. Bohan, G. L. House, J. Imaging Science and Tech., 38, 32 (1994)) because of the high front surface reflectance of these thin emulsions (Research Disclosure 25330, May, 1985). Thus, when these ultrathin tabular grain emulsions are employed in so-called "successive layer" structures that are conventionally employed in color photographic materials, such as for example when a support has provided successively thereon a red-sensitive layer, a green sensitive layer, and a blue sensitive layer, either a loss in speed or a diminution in another important photographic property would be expected to result. It would be expected that the well-known high reflectance of thin tabular grains would lead to deterioration in graininess because larger projected area emulsions having poor graininess would be required to overcome the speed deficit expected from the light loss caused by reflectance. Further, image sharpness would be expected to degrade because of the multiple reflectances that would occur within the photographic element (internal reflectance) (J. Imaging Science and Tech., 38, 32 (1994) and U.S. Pat. No. 5,290,674). Degradation of speed in layers underlying the layers containing the ultrathin tabular grains, degradation in granularity of these underlying layers, and degradation in multilayer acutance would be expected because of this reflectance thereby voiding the advantage of high specularity of transmitted light.
Daubendiek et al U.S. Pat. 4,672,027 reports a 3 mole percent iodide tabular grain silver bromoiodide emulsion having a grain thickness of 0.017 micrometer and thin tabular grain high chloride emulsions are disclosed by Maskasky U.S. Pat. No. 5,217,858 but the advantages of their use in a multilayer application are not recognized.
It would be desirable to have a multilayer photographic element which exhibits an enhanced combination of speed, graininess, and sharpness even when low levels of imaging silver are present in the element.